A typical microelectromechanical systems (MEMS) microphone package includes a substrate, such as an FR-4 based printed circuit board (PCB), a MEMS microphone die attached to the substrate and a cup-shaped lid or cover that is attached to the substrate to create a chamber, within which the microphone die is protected from environmental insults. The lid or the substrate defines an aperture, through which sound enters the chamber. For example, the substrate may define a through-hole under the microphone die. The microphone die detects the sound and generates corresponding electrical signals. In some implementations, other dies are co-located with the microphone die within the chamber, such as to process the electrical signals generated by the microphone die. The package typically includes electrical contact pads on the bottom surface of the substrate, by which the package can be mechanically and electrically connected to a circuit board, such as by solder or electrically conductive adhesive.
MEMS microphones are commonly used in mobile telephones, laptop computers, voice recorders and other electronic devices. These devices are typically made by placing printed circuit boards inside plastic housings. Often, the housings include user interface buttons or thin membranes, with which users may actuate electrical switches mounted on the printed circuit boards. The housings usually define ports (holes) adjacent the MEMS microphone packages, so the users' speech may enter the housing and be detected by the microphones.
Ergonomic considerations typically lead to microphone ports being located on thin sides, rather than on broad flat surfaces, of the electronic devices. For example, on a mobile telephone, the microphone port is typically located on the thin lower side of the telephone, near the bottom row of dial buttons. Because the main circuit board of the mobile telephone is co-planar with the front of the telephone, i.e., with the plane of the dial buttons, the MEMS microphone package is mounted on a differently oriented auxiliary circuit board (a “daughter board”), so as to orient the aperture of the MEMS microphone package in line with the port, i.e., along an axis that is parallel to the main circuit board.
The height of the resulting structure (i.e., the MEMS microphone package and daughter board) poses problems, because the electronic device must be thick enough to accommodate the height of the structure within the device housing. Demand for ever thinner mobile telephones and other electronic devices translates into a demand for a lower profile solution to mounting MEMS microphone packages on circuit boards.
U.S. Pat. No. 6,781,231 to Minervini, which is hereby incorporated by reference, discloses a MEMS microphone package in which an aperture is defined in a side of the microphone package lid. When the resulting side-ported MEMS microphone package is mounted on a main circuit board of a mobile telephone, the axis of the microphone package aperture is oriented in line with the telephone housing microphone port, and the MEMS microphone package presents a low profile. However, defining apertures in the sides of package lids is difficult and expensive and poses other problems.